Agniveshyagrihyasutra 2.4.4

Now, one who considers himself as if impure should sacrifice with the Kūṣmāṇḍa verses; just as a thief, just as an embryo-slayer, even so becomes he who sheds semen in an improper receptacle.

Here, if semen should fall during a dream, or if he is lusting for a woman,

On the new moon or on the full moon, having had hair, beard, body-hair, and nails shaved, bathed, wearing pure garments, he undertakes a vow in the manner of a Vedic student for a year, a month, twenty-four days and nights, twelve nights, six nights, or three nights.

He should not eat meat, he should not approach a woman, he should not sit upon an elevated place, and he should refrain from untruth.

Living on milk is the first rule.

Or, consuming barley gruel, he should perform the twelve-night kṛcchra penance.

Or he may beg for alms.

A Kṣatriya [should consume] rice gruel, a Vaiśya curds.

In the morning, having brought forward and added fuel to the fire according to the rule of cooked sacrifices, having offered with clarified butter verse by verse with these three sections: "Whatever offense to the gods, O gods...", "If not gambling, a debt I have incurred...", and "Bestowing upon you life from all sides...", having offered the four oblations: "In the lion, in the tiger, and what in the adder...", having offered the four oblations: "O Agni, turning back...", "O Agni, Angiras...", "Back with strength...", "Along with wealth...", with kindling-stick in hand, the sacrificer, standing in his place, having reverenced with the twelve-verse hymn: "To Vaiśvānara we announce...", [and reciting:] "Whatever sin has ever been committed by me in mind or speech,

from all that deliver me, being gracious; for you know the truth, svāhā!" — having laid on the kindling-stick, he gives a choice gift.

The rites from the Jaya offerings up to the giving of the choice cow are established.

Having attended [the sacred fire] in a single fire alone; then, at the establishment of the sacred fires, having offered a full oblation with "Whatever offense to the gods, O gods...", "If not gambling, a debt I have incurred...", and "Bestowing upon you life from all sides..."; when intending to begin the Agnihotra, having offered the Daśahotṛ formula; when intending to begin the new and full moon sacrifices, having offered the Caturhotṛ formula; when intending to begin the Cāturmāsya, having offered the Pañcahotṛ formula; at an animal sacrifice, the Ṣaḍḍhotṛ formula; at a Soma sacrifice, the Saptahotṛ formula.

"At the beginning of rituals, one should offer with these," so it is known; for such is the Brāhmaṇa passage, such is the Brāhmaṇa passage.